1. Field of the Invention
The invention relates to a heater control unit and a vehicle seat heater. More particularly, the invention relates to a heater control unit that provides rapid heating ability according to an environmental temperature at startup of a heater provided in a seat, and also to a vehicle seat heater provided with this heater control unit.
2. Description of Related Art
Seat heaters that are provided with a heating element in a sitting surface portion or a backrest of a seat of a vehicle or the like that warms a seated person are being used. With many of these kinds of seat heaters, the temperature is adjusted by changing the amount of power supplied to the heating element, or turning the power to the heating element on or off. For example, Japanese Patent Application Publication No. 2009-283333 (JP 2009-283333 A) describes a heater control unit that keeps an object to be heated at a target temperature by detecting the temperature of a heater, comparing this detected temperature with a target temperature determined beforehand, and controlling a on/off operation of power to the heater. There are also cases in which means for promoting a temperature increase when the heater is turned on (i.e., at startup of the heater) is provided in order to warm a seated person quickly. For example, WO2007/097445 describes a heater unit and the like having excellent rapid warming ability at startup, by providing two heaters and a temperature control unit that controls on/off control that controls the power on or off depending on the temperature.
The heater control unit described in JP 2009-283333 A is provided with a heater, temperature measuring means, temperature controlling means, and an operating switch for starting operation. Turning on the operating switch causes the temperature controlling means to start operation. Then an object to be heated is maintained at a target temperature by comparing a detected temperature obtained from the temperature measuring means with a target temperature determined beforehand, and controlling an on/off operation of power to the heater. Also, the heater control unit described in JP 2009-283333 A may be referred to as an example of related heater control. In this related example, when an operating switch is turned on, a heater is powered up and a timer starts, and the temperature of the heater is detected. Then the detected temperature is compared to a target temperature, a timer time limit is calculated, and when the timer time limit is reached, control is performed to turn off the power supply of the heater. Here, the timer time limit (i.e., the time for which power is supplied, also referred to as the “power-on time”) is obtained by the difference between the detected temperature and the target temperature (see FIG. 6 of JP 2009-283333 A). Applying this kind of control method makes it possible to automatically adjust the time that power is supplied to the heater after activation, according to the temperature difference between the detected temperature and the target temperature. However, with a method that controls the power-on time at startup of the heater according to the difference between the detected temperature and the target temperature, the heat provided to a person seated in the seat (i.e., a seated person) may be too much or too little depending on the temperature of the outside air, which is problematic. For example, when uniformly controlling the power-on time or the amount of power at startup from the seat temperature and the target temperature, a seated person may not be sufficiently warmed when both the outside air temperature and the seat temperature are low. Also, when the seat temperature is low but the outside air temperature is high, the seated person may end up being warmed excessively. In particular, with a vehicle seat, there is often a large difference between the temperature of the environment outside the vehicle and the seat temperature inside the vehicle cabin, and a seated person who had been outside the vehicle needs to be heated appropriately when the heater is turned on (i.e., is started up). Also, with the heater unit described in WO2007/097445, the amount of electric power is increased to improve rapid heating ability, by turning on one heater until a certain temperature is reached (i.e., until a thermostat operates) when the heater is started up. However, two heaters must be provided together, which makes the structure complex. Furthermore, the connective state of the heaters changes according to the thermostat provided in the seat, so the heat at startup may end up being excessive or insufficient due to the relationship with the outside air temperature.